Segmented nut

ABSTRACT

A segmented nut is formed by three segments held together with a surmounting sleeve. Rotation of the sleeve in the order of 60° frees the segments, allowing for quick release of the nut.

FIELD OF THE INVENTION

The present invention relates to a segmented nut or split nut, for usein conjunction with a bolt, allowing for quick release of the nut fromthe bolt.

BACKGROUND TO THE INVENTION

The use of threaded nuts to tighten onto bolts is well known. In aconventional fashion nuts are tightened by threaded rotation in onedirection, and loosened by threaded rotation in the other direction.

In some environments conventional loosening of nuts becomes difficult orimpossible. Over time a nut can bind to a bolt, or have corrosion orother damage done to the thread of the nut and/or bolt, particularly tothe exposed section of the thread, which prevents nut removal.Frequently it becomes necessary to cut the nut away, mechanically or byuse of an oxyacetylene torch or similar. Such an action is timeconsuming, and can raise significant safety concerns.

In other situations the nut may loosen to an extent, but there may besufficient friction between nut and bolt for applied rotation to the nutto cause rotation of the nut-and-bolt together. It can be difficult ortime consuming to restrain a head of the bolt while removing the nut.Indeed, in some situations there may be intervening structures betweenthe bolt head and the nut, meaning that removal of the nut becomes atwo-person operation, requiring coordination and sometimes the erectionof access platforms. To avoid this situation, many industrialenvironments dictate cutting of a nut as standard practice.

In addition to man-power and safety concerns, other adverse consequencescan arise from the requirement to cut nuts using oxyacetylene torches.It is often desirable to use anti-rotation devices, such as a polymerinsert (a ‘nyloc’) within a nut. In environments where oxyacetylenecutting of nuts is required, the use of such inserts is banned, andother solutions for anti-rotation problems must be found.

Segmented nuts, being nuts formed in two or three circumferentiallyarranged pieces, are known. In one common type, the pieces are connectedby thin webs. This allows a segmented nut to function as a normal nutduring fastening, but allows it to be readily broken into pieces forquick removal. This is considered particularly advantageous in adverseenvironment conditions such as those described above.

This type of segmented nut has limitations. In particular, it can bedifficult to achieve an appropriate balance between the strengthrequired to maintain the nut in position in use, and the ease with whichthe webs can be broken for removal.

Another known type of segmented nut is formed from circumferentiallyarranged pieces held together by a surrounding collar. In this nut, thecollar contains clamping screws which apply a radial force to the nutsegments, forcing them together. Release of the clamping screws allowsradial movement of the nut pieces away from the bolt. The threads of theclamping screws in these bolts can suffer the same problems as the nutthreads, being liable to corrode or otherwise seize within the collar.Additionally, they are necessarily considerably smaller than the nut andthus require an additional degree of dexterity and finesse to remove.This is not always convenient or indeed possible.

In an alternative design, attempts have been made to form a segmentednut from circumferentially arranged pieces held together by an axiallymoveable collar. In such a design, the idea is that the collar is slidin an axial direction in order to release the nut pieces. Such nuts arehighly problematic, in use. It can be difficult to achieve sufficientpurchase on the sleeve in order to provide a suitable axial force. Incorrosive environments the necessary axial force can be considerable,and as will be appreciated applying axial forces to an annular surfacein a confined space can be difficult if not impossible.

The present invention seeks to address some of the limitations of priorsegmented nuts.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided asegmented nut having at least two sections, each section having aconcave internal surface and an outer surface, such that the sectionscombine to form an inner nut having a cylindrical internal surface whichis threaded and an outer surface; the segmented nut also including asleeve arranged to locate around the inner nut, the sleeve being movableby rotation between a locked position and a release position, the sleevehaving an internal surface having at least one bearing surface arrangedto bear against the inner nut when in the locked position and thusmaintain the sections in fixed relationship to each other, and whereinmovement of the bearing surface relative to the inner nut causes thesleeve to move into the release position in which at least one sectionis able to move in a radial direction.

In a preferred embodiment, the movement of the sleeve from the locked tothe release position is generally in a tightening direction of the nut.

Alternatively, the movement of the sleeve from the locked to the releaseposition may be generally in a loosening direction of the nut.

It is preferred that the rotational movement is not threaded rotation.

The movement of the sleeve from the locked to the release position maybe rotation of the sleeve relative to the inner nut. Alternatively, themovement of the sleeve from the locked to the release position may be inan axial direction, preferably towards a head of a bolt or otherworkpiece. It is also possible that the movement may be for rotation andaxial movement, for instance using threaded engagement between the innernut and the sleeve.

The movement of the nut section in a radial direction may be by adistance greater than the depth of the thread on the inner surface ofthe inner nut. Alternatively, the nut section may be constrained to moveless than this distance.

In one embodiment of the invention, the outer surface of the inner nutand the internal surface of the sleeve are generally polygonal in crosssection. It is preferred that the polygon defined by the internalsurface of the sleeve is larger than that defined by the externalsurface of the inner nut, such that when the two polygons are parallelthe sleeve is spaced from the inner nut. The distance between opposedsides of the polygon defined by the inner surface of the sleeve is lessthan the distance between opposed vertices of the outer surface of theinner nut. In this way the bearing surfaces of the sleeve may be locatedalong each side of the polygon defined by the internal surface of thesleeve. It is preferred that the bearing surfaces are about midway alongeach side of this polygon.

The vertices of the polygon defined by the external surface of the innernut may be rounded, for instance so as to be part-cylindrical about acentral axis of the inner nut. In this embodiment, it is preferred thatthe bearing surfaces of the sleeve are rounded to be complementary insize and shape to the rounded vertices. Advantageously, this allows forbearing between the sleeve and the inner nut to occur over a face,rather than in a single line. The rounded bearing surfaces may extendcircumferentially about 5° to 10°.

Alternatively, the vertices of the polygon defined by the externalsurface of the inner nut may be part-hexagonal. Advantageously, thisallows for the inner nut to have a periphery which can be readilygrasped by common tools.

Preferably, each side of the polygon defined by the external surface ofthe inner nut is concave. Preferably each side of the polygon defined bythe internal surface of the sleeve is convex. Advantageously, when thesleeve is in the locked position there is therefore a generallytriangular gap between each side of the inner nut and an associatedvertex of the sleeve.

The polygons of both the inner nut and sleeve are preferably regularhexagons.

It is preferred that movement between the locked and release positionscan be effected by rotation through less than 90°. It is furtherpreferred that this movement can be effected through less than 45°. Itis still further preferred that this movement can be effected throughless than 30°. In a most preferred embodiment, movement between thelocked and release positions can be effected by rotation through anangle in the order of 10°.

Preferably, the nut is assembled by press fitting the sections into thesleeve in the locked position. The inner nut and/or the sleeve mayinclude deformable portions such as burrs which assist to hold thesections in rotational position once assembled. The internal thread ofthe inner nut may be formed in the threads prior to assembly, or may bemachined into the inner nut following assembly.

Advantageously, the nut can be assembled during manufacture, with nofurther assembly required before use.

It is preferred that the nut include a plurality of gaps between theinner nut and the sleeve when in the locked position. These gaps may befilled with a potting material such as silicone to assist in maintainingthe nut in the locked position, and/or to prevent the ingress of debrisinto the gaps.

A holding pin may be provided to locate within at least one gap toassist in maintaining the nut in the locked position. The pin may beassociated with an outer grasping portion enabling the pin to be pulledin an axial direction out of its gap, prior to releasing the nut.Alternatively, the sleeve or the inner nut may include a pin receivingrecess into which the pin can be pushed out of its gap.

The nut may be provided with a torque applying tool arranged to providetorque to the inner nut via the gaps.

The inner nut sections may each include a collar section at an outer endthereof, arranged to form an annular collar when the inner nut isassembled. The annular collar preferably has an outer diameter greaterthan the distance between opposed sides of the sleeve, and may act as alip to assist in locating the sleeve in a desired axial positionrelative to the inner nut. The collar may also provide a surface whichcan be gripped during machining of the nut.

The inner nut may have an axial length inside the sleeve similar to thatof the sleeve. Alternatively, the inner nut may have an axial lengthgreater than that of the sleeve. In such an embodiment the inner nut mayhave an extending portion axially adjacent the sleeve, preferablypermitting grasping of the inner nut by a standard tool such as aspanner or socket.

The threaded portion of the inner nut may extend through the entire nut.Alternatively, the threaded portion of the inner nut may have an axiallength less than or equal to that of the inner sleeve. Preferably thethreaded portion of the inner nut is within the axial extend of theouter sleeve.

The sleeve may have a polygonal outer surface suitable for grasping witha standard tool such as a spanner. Alternatively, the sleeve may have anon-polygonal outer surface, such as a circular outer surface, withgrasping surfaces provided for use with a dedicated tool.

The nut may include a biasing means arranged to urge the sections apartwhen in the release position. The biasing means may be formed by aconical washer compressed, in use, within the annular collar.Alternative biasing means could include the use of springs such as leafsprings located between adjacent sections.

The inner nut may include a non-threaded portion an outer edge thereofarranged to receive an anti-rotation device such as a ‘nyloc’ insert.The anti-rotation device may be cut into segments corresponding to thenut sections. Thus cutting could be done, for instance, during machiningof the internal thread. Alternatively, the cutting could be done duringapplication of the insert.

In an alternative embodiment of the invention, the outer surface of theinner nut and the internal surface of the sleeve may both be generallycylindrical, and threaded in a complementary fashion. In this embodimentit is preferred that the threads of the internal surface of the sleeveare oriented in the opposite direction to those of the internal surfaceof the sections; that is, that the threads of the sleeve are ‘lefthanded’ whereas those of the internal surface of the sections are ‘righthanded’.

The complementary threads may be tapered, rolled or otherwise arrangedto reduce any wedging effect caused as the sections begin to separatewhile still being held together at an inner end.

The sections may have an axial length greater than that of the sleeve.In this way, the nut may be tightened by use of a spanner directlyaround the sections, rather than around the sleeve.

BRIEF DESCRIPTION OF THE DRAWINGS

It will be convenient to further describe the invention with referenceto preferred embodiments of the present invention. Other embodiments arepossible, and consequently the particularity of the following discussionis not to be understood as superseding the generality of the precedingdescription of the invention. In the drawings:

FIG. 1 is a perspective of a segmented nut in accordance with a firstembodiment of the present invention;

FIG. 2 is an end view of the segmented nut of FIG. 1;

FIG. 3 is a side cross section of the segmented nut of FIG. 1;

FIG. 4 is an exploded view of a segmented nut in accordance with asecond embodiment of the present invention;

FIG. 5 is an end view of the segmented nut of FIG. 1;

FIG. 6 is an enlarged view of a bearing surface shown in FIG. 5;

FIG. 7a is an end view of the segmented nut of FIG. 1 shown in a lockedposition;

FIG. 7b is an end view of the segmented nut of FIG. 1 shown in a releaseposition;

FIG. 7c is an end view of the segmented nut of FIG. 1 shown in a freeposition;

FIG. 8 is a view of a nut section in accordance with a third embodimentof the present invention;

FIG. 9 is a side cross section along the nut section of FIG. 8;

FIG. 10 is a portion of a tool for use with the segmented nut of FIG. 1;

FIG. 11 is a segmented nut in accordance with a fourth embodiment of thepresent invention;

FIG. 12 is a perspective of the segmented nut of FIG. 11, shown duringrelease;

FIG. 13 is a segmented nut in accordance with a fifth embodiment of thepresent invention;

FIG. 14 is an exploded view of the segmented nut of FIG. 13;

FIG. 15a is a segmented nut in accordance with a sixth embodiment of thepresent invention;

FIG. 15b is a side cross section of the segmented nut of FIG. 15 a;

FIG. 16a is a segmented nut in accordance with a seventh embodiment ofthe present invention;

FIG. 16b is a side cross section of the segmented nut of FIG. 16 a;

FIG. 17a is a segmented nut in accordance with an eighth embodiment ofthe present invention;

FIG. 17b is a side cross section of the segmented nut of FIG. 17 a;

FIG. 18a is a segmented nut in accordance with a ninth embodiment of thepresent invention;

FIG. 18b is a side cross section of the segmented nut of FIG. 18 a;

FIG. 19a is an enlarged view of a portion of an inner nut from withinthe segmented nut of FIG. 15 a;

FIG. 19b is a further enlarged view of the circled portion of FIG. 19 a;

FIG. 20a is a view of a nut section in accordance with a tenthembodiment of the present invention;

FIG. 20b is an end view of a nut formed using the nut sections of FIG.20 a;

FIG. 21a is an end view of a nut in accordance with an eleventhembodiment of the present invention, shown in a locked position;

FIG. 21b is an end view of the nut of FIG. 21a , shown in a releaseposition;

FIG. 22a is an end view of a nut in accordance with a twelfth embodimentof the present invention, shown in a locked position;

FIG. 22b is an end view of the nut of FIG. 22a , shown in a releaseposition;

FIG. 23a is an end view of a nut in accordance with a thirteenthembodiment of the present invention, shown in a locked position; and

FIG. 23b is an end view of the nut of FIG. 23a , shown in a releaseposition.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to the Figures, FIGS. 1 to 3 show a segmented nut 10 formed bythree nut sections 12 and an outer sleeve 14.

Each nut section 12 extends through an arc of 120°, with a concave innersurface and a generally convex outer surface. When placed together, asshown in FIGS. 1 to 3, the nut sections 12 combine to form an inner nut16. The inner nut 16 has a cylindrical internal bore 18, formed by theconcave inner surfaces, which is threaded (in this case using aconventional tapered v-thread) so as to be received about the threadedend of a bolt or other externally threaded member.

The inner nut 16 has an outer surface 20 which is generally polygonal incross section, being based on a regular hexagon in the embodiment shown.Each of the generally convex outer surfaces of the nut sections 12includes one full hexagon side, and two half hexagon sides.

The outer sleeve 14 is generally annular in cross section, with aninternal surface 22 and an external surface 24. Both the internalsurface 22 and the external surface 24 have a cross sectional shapebased on a regular hexagon, with the internal surface 22 being larger indimension than the outer surface 20 of the inner nut 16.

The outer sleeve 14 has an axial length approximately half that of theinner nut 16. This means that the inner nut 16 has an extending portion26 which extends from the outer sleeve 14 to an outer end of the nut 10.The extending portion 26 has an outer surface 28 which is a true regularhexagon, adapted to be engaged by a conventional spanner or socket.

The inner nut 16 also includes a radial collar 30 located, in use, at aninner end of the nut 10 adjacent the sleeve 14. The radial collar 30 isannular, with an external radius greater than the distance betweenopposed sides of the sleeve 14. The sleeve 14 is thus prevented frommoving axially past the collar 30.

FIG. 4 shows an alternative segmented nut 50. The segmented nut 50 hasno extending portion 26; that is, the axial length of the inner nut 16is equal to that of the outer sleeve 14 plus the collar 30.

The precise nature of the cross sectional shapes of the inner nut 16 andouter sleeve 14 can be seen with reference to FIGS. 5 and 6.

In the outer surface 28 of the extending portion 26, each of thehexagonal sides is flat. In the outer surface 20 of the inner nut 16within the sleeve 14, each of the hexagonal sides is concave, beingaligned with the corresponding surface 28 of the extending portion alongthe centre of each hexagon side and curving away from the line of thesurface 28 towards each hexagon vertex 32.

The distance from a centre line of the inner nut 16 to a vertex 32 ofthe regular hexagon defined by the outer surface 28 is thus less thanthe distance from the centre line to a nominal vertex of thehexagon-based shape defined by the outer surface 20.

The inner nut 16 is machined or otherwise formed during assembly to fitwithin a cylindrical bore having a radius greater than the distance fromthe centre line to the vertex 32 of the regular hexagon, but less thanthe distance to the nominal vertex of the hexagon-based shape defined bythe outer surface 20. In effect, this means that the vertices of outersurface 20 form convexly rounded bearing surfaces 34. The bearingsurfaces 34 are each part cylindrical, having a radius of curvatureequal to their actual radius relative to the centre line. Each bearingsurface 34 extends through an arc of about 5° to 10°.

In the internal surface 22 of the sleeve 14, each of the hexagonal sidesis convex, with each side 36 protruding inwardly towards a centre of thesleeve 14. The distance between the most inward part of one side 36 (atits centre) and that of an opposed side 36 is greater than the distancebetween opposed vertices 32 of the outer surface 28 of the inner nutextending portion 26, and less than the distance between opposed nominalvertices of the hexagonal-based shape of the inner nut 16.

The internal surface 22 of the sleeve 14 is machined or otherwise formedduring assembly to define edges of a cylindrical bore having a radiusequal to that of the bearing surfaces 34. This means that the mostinward part of each side 36 is machined to form a concave roundedbearing surface 38. The bearing surfaces 38 are each part cylindrical.

In the embodiment shown, the inner nut is threaded with a tapered v-typescrew thread. This is the most common type of thread used for industrialfasteners. In use, as a torque is applied to the nut, a tension isinduced in the thread of the nut and a corresponding radial force isgenerated on the each of the inner nut segments, 12, which in turn areconstrained by radial forces of the sleeve 14, and which manifest as ahoop stress in the sleeve 14. This arrangement is desirable as thecontact pressure between the sleeve 14, and the inner nut segments 12,tends to increase as the tension of the nut is increased and thereforethe sleeve 14, is held more firmly in place as the nut tension isincreased.

In the embodiment shown, the inner bearing surface 38, of the sleeve andthe outer bearing surface of the inner nut 34, contact along a generallycircumferential contact patch. This arrangement ensures that forcesgenerated by the inner nut segments 12 on the outer sleeve 14 arepredominately or purely of a radial nature and do not induce a torque onthe outer sleeve

The segmented nut 10 is formed by press fitting the sections 12 into theouter sleeve 14 such that the bearing surfaces 34 of the inner nut 16bear against the bearing surfaces 38 of the sleeve 14.

It will be appreciated that the press fitting causes the bearingsurfaces 34 to act against the bearing surfaces 38 in a radial direction(subject to manufacturing tolerances).

Whilst the radius used for surface 34 and surface 38 may be identical,it will be appreciated that different combinations may be used toprovide a degree of control of the release torque required to rotate theouter sleeve 14, to achieve release of the nut 16. Furthermore thecircumferential extent of the surfaces 34 and 38 may be chosen toachieve certain characteristics in the required release torque, and/orthe release angle of the outer sleeve. For example by having a smallercircumferential extent of the surface 34 an increased pressure loadingwill occur on this surface and therefore an increased release torquewill be required.

A generally bell shaped gap 40 is formed between each vertex of theinternal surface 22 of the sleeve 14 and an associated side of thehexagon-based outer surface 20 of the inner nut 16.

FIGS. 7a to 7c show sequential rotation of the sleeve 14 relative to theinner nut 16.

In a locked position, as shown in 7 a as well as FIGS. 1 and 2, thebearing surfaces 34 and 38 are pressed against each other, creating africtional engagement which prevents relative rotation.

When a sufficient torque (for example in the nut tightening direction)is applied to the outer sleeve 14 while the inner nut is held relativelystationary, the sleeve 14 will rotate relative to the inner nut 16. Whenthe sleeve has rotated about 10°, this will be sufficient for thebearing surface 38 of the sleeve 14 to pass the bearing surface 34 ofthe inner nut 16. This is shown in FIG. 7 b.

At this position the restraining engagement between bearing surfaces 34and 38 ceases, and the sleeve is in a release position. From here it canbe freely rotated without restraint into a free position as shown inFIG. 7c , being a total rotation of 30°.

In the free position as shown in FIG. 7c there is no force holding thenut sections 12 together, leaving each one free to move radiallyoutwardly.

In a preferred embodiment, the clearances are such that in the freeposition of FIG. 7c the nut sections 12 are able to move in a radialdirection by a distance greater than the depth of the thread on theinternal surface of the bore 18 of the inner nut 16. This means that inthe free position the nut sections 12 may be moved outside the thread ofa bolt onto which the inner nut 16 has been threaded. The released nutsections 12 may then be slid over the bolt in an axial direction.

In an alternative embodiment, the clearances may be tighter and the nutsection 12 may be constrained to move in a radial distances less thanthe depth of the thread on the internal surface of the bore 18 of theinner nut 16. In this embodiment, the released nut sections retainthreaded engagement with a bolt, with the effect of release being toloosen the inner nut 16.

It will be observed that the rotational movement of the sleeve 14relative to the inner nut 16 is not over threads. This means that thenut 10 can be released without any part requiring movement along athread. This is considered highly desirable, particularly in causticenvironments. It will be further observed that the outer sleeve is alsonot required to move along any exposed surface. This is also consideredhighly desirable.

In order to assist the radial outward movement of the nut sections 12,the segmented nut 10 includes a biasing means, in this embodiment beinga conical washer 42 arranged to be pressed into the collar 30 duringtightening of the nut 10 in use. The conical washer 42 is arranged tourge the sections 12 apart when the sleeve 14 is rotated into therelease position. The conical washer may also be used without the needof a collar incorporated into the inner nut design, for example theconical washer may be used in conjunction with the embodiments shown inFIGS. 15, 16 & 17.

In order to guard against inadvertent movement of the sleeve 14 into therelease position, some embodiments of the invention propose the use of apin 44. In the embodiment of FIG. 1, a pin 44 is located in a slotmachined into one of bearing surfaces 34. The pin 44 has an axial lengthabout one third that of the sleeve 14. The inner nut 16 includes anaxially aligned recess 46 located behind the pin 44. The arrangement issuch that the pin 44 can be pushed from outside the sleeve 14 into therecess 46, allowing rotation of the sleeve 14.

An alternative pin 52 is shown in the embodiment of FIG. 4. This pin 52has a body portion 54 shaped to locate within a gap 40, and an armportion 56 arranged to locate outside the sleeve 14. The pin 52 can beremoved by engaging the arm portion 56 and pulling the pin out.

A further embodiment of the present invention is shown in FIGS. 8 and 9.FIGS. 8 and 9 show a nut section 60 similar to the nut section 12 of thefirst embodiment. The nut section 60 has an additional outer flange 62,arranged to be bent inwardly to form a circumferential groove 64 at anouter end of the nut section 60. This groove is arranged to receive anylon insert 66 for prevailing torque/anti-rotation purposes.

One method of manufacturing the segmented nut of the present inventionincludes the steps of press fitting the nut sections 12 or nut sections60 into a sleeve 14, and then machining an internal thread within theinner nut 16. It is anticipated that the nylon insert 66 could be cutinto three portions corresponding to the nut sections 60 during thismachining operation.

An alternative method of manufacturing involves forming the threadwithin each nut section 12 before assembly. This could be by stamping,casting, 3D printing, CAD/CAM machining or other suitable process ableto achieve required tolerances. It is considered that such a methodwould enable the provision of otherwise difficult-to-machine threads onthe inner nut, such as a saw-tooth thread or other direction-specificthreads.

It will be appreciated that in embodiments shown it is not desirable toapply a tightening torque to the outer sleeve during application of thenut to a work piece as this may result in a release of the sleeve beforethe required nut tightening torque is reached (i.e. the sleeve releasetorque being reached before the required nut tightening torque has beenreached).

Segmented nuts 10 having an extending portion 26 may be screwed intoposition on a bolt by the use of a spanner or other standard tool on theextending portion 26. Segmented nuts 50 without an extending portion 26may require the use of a dedicated tool for tightening, such as thatshown in FIG. 10. FIG. 10 shows a portion of a tightening tool 70 havingprongs arranged to locate within gaps 40 of the segmented nut 50. Thetool 70 can then be rotated using known means. The tightening tool 70,or a modification thereof (not shown), may also be used with nuts thathave an extended portion 26 as shown in FIGS. 1-3, in which case thetool 70 assists in maintaining the relative position of the sleeve 14,and inner segments 16, during the nut tightening procedure—which mayundergo severe rotational vibrations e.g. during use of a rattle gun.

Rotation of the outer sleeve 14 may be achieved by using a spanner orsimilar tool. This may require the holding of the inner nut, either by asmaller spanner on an extending portion 26 or by a tool 70.

In an alternative embodiment (not shown), the outer sleeve has acylindrical outer surface with apertures or slots into which a dedicatedtool (such as a C-spanner or a hook spanner) may be inserted. This mayreduce the risk of a user inadvertently releasing the segmented nut 10when they intend to tighten it on a bolt.

In the embodiments discussed above it will be appreciated that the outersleeve may be rotated in either direction in order to move to a releaseposition. This provides the user a degree of flexibility in choosingwhich mode of nut release is most appropriate for the circumstances. Forexample, if the nut and thread are generally in good condition, rotationof the outer sleeve in the nut untightening direction may result in thenut being removed from the bolts without the inner nut segments becomingfree. Thus the nut can be removed as a single piece and could, subjectto applicable regulations regarding the re-use of nuts, be re-used. Ifhowever the nut was to become stuck, continued application of torque tothe outer sleeve (and subject to the bolt thread not also rotating)would release the inner nuts. In another embodiment (not shown), thebearing surfaces 34 and 38 are shaped so as to permit movement in onlyone direction. It is anticipated that this will be in the direction oftightening of the nut on the bolt.

In general, the nut 10 of the embodiments disclosed above may bereleased from a bolt in four different ways: by rotation of the outersleeve 14 relative to the inner nut 16 in the tightening direction ofthe nut; by rotation of the outer sleeve 14 relative to the inner nut 16in the loosening direction of the nut (this may require the inner nut 16to be held relatively stationary, for instance by the use of one spanneron the outer sleeve and another on the inner nut); by axial movement ofthe outer sleeve 14 relative to the inner nut 16 (that is, in thereverse of the assembly of the nut 10); and by rotation of the outersleeve together with the inner nut 16 in the loosening direction (thatis, removing the nut 10 as a traditional nut).

It is anticipated that potting material such as silicone or a frangiblematerial may be used within the gaps 40, both to reduce the risk of dustor debris entering the gaps 40 and also to increase the torque requiredto move the sleeve 14 into the release position. This reduces any riskof inadvertent release.

FIGS. 11 and 12 show a segmented nut 110 formed by three nut sections112 and an outer sleeve 114.

Each nut section 112 is part-cylindrical, having an arc of 120°, with aconcave inner surface and a convex outer surface. When placed together,as shown in FIG. 1, the nut sections combine to form an inner nut 116.The inner nut 116 has a cylindrical internal bore 118, formed by theconcave inner surfaces, which is threaded so as to be received about thethreaded end of a bolt or other externally threaded member.

The inner nut 116 has an outer surface 120 which is polygonal in crosssection, being regular hexagonal in the embodiment shown. Each of thegenerally convex outer surfaces of the nut sections 112 includes a fullhexagon side, and two half hexagon sides.

The outer sleeve 114 is annular in cross section, with an internal bore122 and an external surface 124. Both the internal bore 122 and theexternal surface 124 are cylindrical, with the internal bore 122 beingslightly larger in dimension than the outer surface 120 of the inner nut116.

The outer sleeve 114 has an axial length approximately half that of theinner nut 116. The inner nut 116 has an extending portion 126 axiallyadjacent the outer sleeve 114. The extending portion 126 is cylindrical,with an outer diameter less than that of the hexagonal portion of theinner nut 116

In use, the nut sections 112 are placed together to form the inner nut116, and the outer sleeve 114 is slid around the outer surface 120 ofthe inner nut in order to hold the nut sections 112 together. In thisconfiguration, the segmented nut 110 can be applied to a bolt byoperation of a socket wrench or similar about the external surface 120.

When release of the nut is required, the sleeve 114 can be pressedforward on the bolt, over the extending portion 126. This acts torelease the nut portions 112, allowing them to fall away.

FIGS. 13 and 44 show a segmented nut 210 formed by three nut sections212 and an outer sleeve 214.

Each nut section 212 is part-cylindrical, having an arc of 120°, with aconcave inner surface and a convex outer surface. When placed together,as shown in FIG. 3, the nut sections combine to form an inner nut 216.The inner nut 216 has a cylindrical internal bore 218, formed by theconcave inner surfaces, which is threaded so as to be received about thethreaded end of a bolt or other externally threaded member.

The inner nut 216 has a stepped outer surface, with a first portion 220which is cylindrical, and externally threaded, and a second portion 221which is regular dodecagonal in cross section, and smaller in crosssectional dimension than the first portion 220. The threads on the firstportion 220 are oriented in the opposite direction to those of the bore218.

The outer sleeve 214 is annular in cross section, with an internal bore222 and an external surface 224. The internal bore 222 is cylindrical,and internally threaded with threads which are complementary in size andshape to those on the first portion 220 of the outer surface of theinner nut 216. The external surface 224 is regular dodecagonal in crosssection.

The outer sleeve 214 has an axial length approximately half that of theinner nut 216. The axial length of the outer sleeve 214 is approximatelyequal to that of the first portion 220 of the outer surface of the innernut 216.

In use, the nut sections 212 are placed together to form the inner nut216, and the outer sleeve 214 is rotated about the first portion 220 ofthe outer surface of the inner nut 216 in order to hold the nut sections212 together. In this configuration, the segmented nut 210 can beapplied to a bolt by operation of a socket wrench or similar about thesecond portion 221 of the outer surface of the inner nut 216. The torqueapplied to the inner nut 216 will cause rotation of the segmented nut210 about the bolt.

The segmented nut 210 can thus be tightened as much as is desirable.

When release of the nut is required, a further torque can be applied tothe outer sleeve 214, causing it to rotate relative to the inner nut 216until it is removed from the first portion 220. As the threads areoriented in a different direction, releasing rotation of the outersleeve 214 occurs in the same angular direction as tightening rotationof the inner bolt 216. Release of the outer sleeve 214 causes the nutsections 212 to fall apart.

FIGS. 15 to 18 show other embodiments of the segmented nut 10, in whichthe thread within the internal bore 18 is varied for differentapplications.

In each of FIGS. 15 to 18 the inner nut 16 is formed with bearingsurfaces 34 being rounded and with small flat sections 34 a and 34 beither side and extending axially, as shown in FIG. 19. With this shapethe extending portion 26 can be a continuation of the shape of the innernut 16, allowing nut sections 12 to be extruded with constantcross-sectional shape. Further, the inner nut 16 of FIGS. 15 to 17 doesnot use a radial collar 30. The small flat sections 34 a and 34 bprovide a tool engagement surface for use with conventional spannersand/or sockets.

The inner nut 16 of FIG. 15 has an internal bore 18 which is threadedthrough its entire length.

The inner nut 16 of FIG. 16 has an internal bore 18 which has anunthreaded introductory portion. The outer sleeve 14 of FIG. 16 sitsslightly back of an inner end of the nut 10, with the beginning of thethread being arranged to align axially with the outer sleeve 14.

The inner nuts 16 of FIGS. 17 and 18 each have an internal bore 18 wherethe entirety of the threaded portion is within the outer sleeve 14.

It will be appreciated that the loading of the thread of the inner nut16 is largely taken by the first few engaged threads. For this reason,it is considered desirable to ensure that these threads are containedwithin the outer sleeve 14. In this way, load applied via the threadswill act to increase the radial bearing force between the inner nut 16and the outer sleeve 14.

A still further embodiment of the present invention is shown in FIGS.20a and 20b . FIGS. 20a and 20b show a nut section 80 similar to the nutsection 12 of the first embodiment. The nut section 80 has a centralaperture 82, into which a nylon plug 84 may be fitted. The nylon plug 84may act as a prevailing torque/anti-rotation device, negating the needfor the insert described in relation to FIGS. 8 and 9.

Further embodiments of the present invention are shown in FIGS. 21 to23. These figures show a nut where the sides 36 of the sleeve 14 areonly slightly curved, and where the radial distance the nut sections 12can travel on release is greatly diminished relative to the earlierembodiments. It is anticipated that these nut may require the sleeve 14to be moved axially between a narrow release position and a freeposition. These designs allow for a more regular nut shape, such as thehexagonal inner nut of FIG. 22. It also allows for a significantlystronger sleeve with the same outer dimension.

Modifications and variations as would be apparent to a skilled addresseeare deemed to be within the scope of the present invention.

Having described the invention, the following is claimed:
 1. A segmentednut comprising: at least two sections, each section having a concaveinternal surface and an outer surface, such that the sections combine toform an inner nut having a cylindrical internal surface which is atleast partially threaded, and an outer surface; and a sleeve arranged tolocate around the inner nut, the sleeve being movable by rotationbetween a locked position and a release position, the sleeve having aninternal surface having at least one bearing surface arranged to bearagainst the inner nut when in the locked position and thus maintain thesections in fixed relationship to each other, the sections beingmaintained in fixed relationship to each other irrespective of thethreaded engagement of the inner nut when the sleeve is in the lockedposition, wherein movement of the at least one bearing surface relativeto the inner nut causes the sleeve to move into the release position inwhich at least one section is able to move in a radial direction,wherein the cylindrical internal surface is threaded so as to define atightening rotational direction of the nut, and rotation in thetightening rotational direction of the sleeve relative to the inner nutcauses movement of the sleeve from the locked to the release position.2. A segmented nut as claimed in claim 1, wherein the rotationalmovement of the sleeve relative to the inner nut is not along a thread.3. A segmented nut as claimed in claim 1, wherein the sleeve can bemoved into a release position by movement in an axial direction.
 4. Asegmented nut as claimed in claim 1, wherein the at least one section isable to move in the radial direction when in the release position by adistance greater than the depth of the thread on the inner surface ofthe inner nut.
 5. A segmented nut as claimed in claim 1, wherein the atleast one section is constrained to move in the radial direction when inthe release position by a distance less than the depth of the thread onthe inner surface of the nut.
 6. A segmented nut as claimed in claim 1,wherein the movement of the sleeve from the locked to the releaseposition is by axial movement in addition to rotation.
 7. A segmentednut as claimed in claim 1, wherein the outer surface of the inner nutand the internal surface of the sleeve are generally polygonal in crosssection.
 8. A segmented nut as claimed in claim 1, wherein movementbetween the locked and release positions can be effected by rotationthrough less than 90°.
 9. A segmented nut as claimed in claim 1, whereinthe nut is assembled by press fitting the sections into the sleeve inthe locked position.
 10. A segmented nut as claimed in claim 1, whereinthe nut includes a plurality of gaps between the inner nut and thesleeve when in the locked position.
 11. A segmented nut as claimed inclaim 1, wherein the inner nut sections include a collar section at anouter end thereof, arranged to form an annular collar when the inner nutis assembled.
 12. A segmented nut as claimed in claim 1, wherein theinner nut has an axial length greater than that of the sleeve.
 13. Asegmented nut as claimed in claim 1, wherein the sleeve has a polygonalouter surface.
 14. A segmented nut as claimed in claim 1, wherein thesleeve has a non-polygonal outer surface.
 15. A segmented nut as claimedin claim 1, wherein the nut includes a biasing means arranged to urgethe sections apart when in the release position.
 16. A segmented nut asclaimed in claim 1, wherein a bearing force provided by the bearingsurface of the sleeve bearing against the inner nut acts in a radialdirection.
 17. A segmented nut as claimed in claim 1, wherein the nutincludes at least one anti-rotation insert located along the thread ofthe internal surface.
 18. A segmented nut comprising: at least twosections, each section having a concave internal surface and an outersurface, such that the sections combine to form an inner nut having acylindrical internal surface which is at least partially threaded, andan outer surface; and a sleeve arranged to locate around the inner nut,the sleeve being movable by rotation between a locked position and arelease position, the sleeve having an internal surface having at leastone bearing surface arranged to bear against the inner nut when in thelocked position and thus maintain the sections in fixed relationship toeach other, the sections being maintained in fixed relationship to eachother irrespective of the threaded engagement of the inner nut when thesleeve is in the locked position, wherein movement of the at least onebearing surface relative to the inner nut causes the sleeve to move intothe release position in which at least one section is able to move in aradial direction, wherein the sleeve has a plurality of releasepositions.
 19. A segmented nut as claimed in claim 18, wherein therotational movement of the sleeve relative to the inner nut is not alonga thread.
 20. A segmented nut as claimed in claim 18, wherein the atleast one section is able to move in the radial direction when in therelease position by a distance greater than the depth of the thread onthe inner surface of the inner nut.
 21. A segmented nut as claimed inclaim 18, wherein the at least one section is constrained to move in theradial direction when in the release position by a distance less thanthe depth of the thread on the inner surface of the nut.
 22. A segmentednut as claimed in claim 18, wherein the outer surface of the inner nutand the internal surface of the sleeve are generally polygonal in crosssection.
 23. A segmented nut as claimed in claim 18, wherein movementbetween the locked and release positions can be effected by rotationthrough less than 90°.
 24. A segmented nut as claimed in claim 18,wherein the nut is assembled by press fitting the sections into thesleeve in the locked position.
 25. A segmented nut as claimed in claim18, wherein the inner nut sections include a collar section at an outerend thereof, arranged to form an annular collar when the inner nut isassembled.
 26. A segmented nut as claimed in claim 18, wherein the innernut has an axial length greater than that of the sleeve.
 27. A segmentednut as claimed in claim 18, wherein the sleeve has a polygonal outersurface.
 28. A segmented nut as claimed in claim 18, wherein the sleevehas a non-polygonal outer surface.
 29. A segmented nut as claimed inclaim 18, wherein the nut includes a biasing means arranged to urge thesections apart when in the release position.
 30. A segmented nut asclaimed in claim 18, wherein a bearing force provided by the bearingsurface of the sleeve bearing against the inner nut acts in a radialdirection.
 31. A segmented nut as claimed in claim 18, wherein the nutincludes at least one anti-rotation insert located along the thread ofthe internal surface.